Touch panels are used as means for inputting characters and pictures in various electronic devices such as cellular (or mobile) phones and personal computers. The touch panel senses a touch of a hand or a stylus pen and performs signal processing for switching the touch into an electric signal.
When an electronic circuit is disposed in a stylus pen, not only a simple touch input but also a mouse function such as selecting or dragging a part of an image by generating an electric signal from the stylus pen may be performed. In this manner, when the electronic circuit is disposed in the stylus pen, power is required to operate the electronic circuit of the stylus pen. For example, there is a method of supplying power from a battery which is provided in the stylus pen.
On the other hand, recently, a method has been used in which a separate dedicated panel for power supply is provided in a main body of a cellular phone, and necessary power is supplied wirelessly from the separate dedicated panel to the stylus pen.
A power supply technique disclosed in Patent Document JP 4866941 B is performed by a separate power transmission device 4 disposed beneath an LCD module 3 in a smart phone. Here, the power transmission device 4 transmits electric power to a coil inside a stylus pen through an induction coil. That is, in Patent Document 1, the separate power transmission device including an induction coil is disposed beneath the LCD module to supply power to the stylus pen, such that power is transmitted and received through inductive coupling between the coil of the stylus pen and the power transmission device.
However, as described above, the structure that the power transmission device including the induction coil is separately installed beneath the LCD module to supply power to the stylus pen causes an increase in cost and also an increase in a thickness of a cellular phone. When an electrode line of a touch panel is made of a coil, since a resistance component due to the electrode line of the touch panel is large, energy is discharged as heat due to the resistance before the circuit is resonated, and thereby the circuit fails to be resonated.
In order to solve such problems, there is an increasing need for a technology for supplying power to a stylus pen using an existing touch panel and detecting a signal received from the stylus pen, without using a separate power transmission device.